It is known that a fine particle of metal (particle diameter of not larger than 1 μm) has a variety of specific characteristics that any bulk material does not have. Currently, it is greatly expected on a variety of technological applications with making the best use of such the characteristics, in individual fields of such as electronics, bio, energy, or the like.
In particular, it is greatly expected on a fine particle of metal having the particle diameter of not larger than 1 μm and comprised of a metal and/or an alloy thereof for industrial general purpose, such as copper, nickel, cobalt, iron, zinc, tin, silver, or the like, as a formation material for a surface mounted component, such as an electrically conductive circuit, a bump, a via, a pad, or the like, as a magnetic element for a high density magnetic storage medium and for an antenna, and as a catalyst material for a gas modification filter and for an electrode of a fuel cell.
Regarding a method for producing the fine particle of a metal having such a small particle diameter, there are a vapor phase synthesis method and a liquid phase synthesis method. Here, the vapor phase synthesis method is a method to form a fine particle of a metal as a solid state from a metal vapor introduced into a vapor phase. The liquid phase synthesis method is a method to precipitate a fine particle of a metal by reducing a metal ion dispersed into a solution. Moreover, regarding such the liquid phase synthesis method, it is known in general that there are a method using a reducing agent for reducing such the metal ion and a method to perform a reduction electrochemically on a cathode electrode.
Further, in recent years, an attention is focused on a technology that a wiring pattern is formed using an ink-jet method with an ink containing a fine particle of a metal and then a wiring is formed by baking thereof. However, in a case of using the ink containing the fine particle of a metal as ink for the ink-jet, it is important to retain dispersibility in the ink for a long period of time. A method for producing a fine particle of a metal is proposed therefor to retain the dispersibility for the long period of time in the ink.
Moreover, regarding a method for obtaining a metallic thin film or a thin metallic wire, by baking after drying a fine particle dispersion of metal, there are disclosed patent documents as described below.
According to a patent document 1, regarding a method for obtaining a fine particle of copper, there is disclosed an electrically conductive fine layer of copper to be formed by forming a fine particle of copper having a particle diameter of not larger than 50 nm containing palladium in a polyethylene glycol solution or an ethylene glycol solution by adding a palladium ion for nucleation with adding polyethyleneimine as a dispersing agent, by performing a pattern print onto a substrate using such a fine particle dispersion of copper, and then by performing a heat treatment therefor in an atmospheric current of 4% H2—N2 for approximately three hours at a temperature of 250° C.
According to a patent document 2, there is disclosed a pattern of a metal wiring to be obtained by coating ink for a ink-jet onto a substrate using the ink-jet method, which contains a fine particle of a metal oxide having a primary particle diameter of not larger than 100 nm, and then by performing reduction of a cuprous oxide by performing a heat treatment therefor in a hydrogen gaseous atmosphere for approximately one hour at a temperature of 350° C.
According to a patent document 3, there is disclosed a thin film of silver to be produced by coating a nano particle of a metal onto a substrate (a glass) using a spin coat method, on which an organic metal compound as a dispersing agent is attached to around the metal, by drying it at a temperature of 100° C., and then by baking it at a temperature of 250° C.
Furthermore, according to a patent document 4, there is disclosed a thin film of copper to be obtained by concentrating a cuprous oxide to have a concentration of 30% by weight, which is suspended into diethylene glycol, in which secondary particles have a mean particle diameter of 500 nm, by performing further an ultrasonic wave treatment to be electrically conductive ink, by coating it onto a slide glass, and then by heating it in a reducing atmosphere for approximately one hour at a temperature of 350° C.    [Patent Document 1] Japanese Patent Application Publication No. 2005-330552    [Patent Document 2] Japanese Patent Application Publication No. 2004-277627    [Patent Document 3] Japanese Patent Application Publication No. 2005-081501    [Patent Document 4] Japanese Patent Application Publication No. 2004-323568